I. Technical Field
The present disclosure relates to new methods for the epoxidation of olefins.
II. Description of Related Art
Propylene oxide is a colorless volatile liquid and is produced on a large scale industrially. Its major application includes the production of polyether polyols for use in making polyurethane plastics. Generally, there are three major commercial processes employed for the production of propylene oxide. One process is based on chlorohydrin technology (Scheme 1). Another utilizes the epoxidation of propylene with hydroperoxides. The third uses hydrogen peroxide to epoxidize propylene.

Hydroperoxide epoxidation of propylene requires an air oxidation of ethyl benzene or isobutane in a separate prior step to produce ethylbenzene hydroperoxide or tert-butylhydroperoxide, respectively, which is then reacted with propylene in the presence of a catalyst (such as soluble molybdenum supported titanium) to produce propylene oxide and the co-products alpha-methyl benzyl alcohol (1-ethylphenyl alcohol or MBA) and t-butyl alcohol, respectively (Scheme 2).

The oxidation of propylene via cumene hydroperoxide was commercialized by Sumitomo Chemical. This process is also in the hydroperoxide class. Cumene hydroperoxide is pre-formed in a separate step (autoxidation of cumene), which is the same as ethylbenezene and isobutene oxidation described above, except in this case the coproduct cumyl alcohol produced from the epoxidation is converted back to cumene via hydrogenolysis.

Utilizing hydrogen peroxide, BASF and Dow Chemical developed a process to produce propylene oxide by oxidizing propylene with aqueous hydrogen peroxide in methanol solution using titanium silicate catalysts (TS1) in 2009.
In the 1990's a process for the production of H2O2 via alpha-methylbenzyl alcohol (1-phenylethyl alcohol or MBA) oxidation, which involved the formation of acetophenone as a co-product, was developed by Lyondell Chemical Company. At that time there were no good catalysts for the epoxidation of propylene with hydrogen peroxide. Later, TS1 was shown to be an efficient catalyst for the epoxidation of propylene using H2O2, but it requires a methanol solvent to be effective. Since methanol is a small molecule, it will react with propylene oxide to yield undesirable ring opening byproducts such as 1-methoxy-2-propanol or 2-methoxy-1-propanol. In addition, water, which is also used as a cosolvent in most cases, will also react with propylene oxide to yield propylene glycol as a byproduct. In both situations, propylene oxide yield will be reduced because of the ring opening side reactions taken place.